Vaporization and combustion process for hydrocarbon distillates



ET AL 2,661,271

M52112 Mfdv j;

E. C. HYATT VAPORIZATION AND COMBUSTION PROCESS FOR HYDROCARBON DISTILLATES Filed April 13, 1948 Dec. 1, 1953 Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE VAPORIZATION AND COMBUSTION PROCESS 1 FOR HYDROCARBON DISTILLATES poration of Kansas Application April 13, 1948, 'Serial No. 20,644

Claims. (Cl. 48212) This invention relates to vaporization and combustion process for hydrocarbon distillates. It is applied generally to systems in which hydrocarbon distillate fuels are vaporized and then used in a combustion or chemical process. The invention is effective in the vaporization and combustion of straight run hydrocarbon distillates, but is particularly useful in the vaporization and combus tionof cracked fuels, such as c'atalytically cracked and thermally cracked or reformed hydrocarbon distillates, or any combination thereof.

Distillate fuel oils are classified generally, for commercial purposes, in two groups: straight run fuels, by which we mean fuels that are produced essentially by distillation processes alone; and cracked fuels, by which we mean fuels produced by thermal, catalytic or reforming processes.

The general problem is that of utilizing hydrocarbon distillate fuels for chemical or combustion processes without producing excessive formations of carbon, asphaltic or tarry-like residues, soot or smoke. The widespread use of cracking proc esses for the production of high octane gasolines has resulted in greater supplies of the by-product distillate fuels originating from these cracking processes. Many dirficulties have been experienced because these cracked fuels form much greater quantities of undesirable residues during vaporization and combustion than do straight run fuels.

To cite a specific example of dilficulties encountered, excessive vaporization and combustion residues were produced when a cracked fuel was used in a common pot-type vaporizing oil burner. Less vaporization and combustion residues were produced when a straight run fuel was used in this burner.

Similar difficulties are experienced with other types of oil burners, diesel engines, and other oil-burning devices. The greatly increased use of oil-burning devices has caused fuel shortages, particularly of straight run fuels. By blending straight run and cracked fuels, a mixture is available that performs somewhat more satisfactorily than the original cracked fuels; however, the fundamental di'ffi'culties still remain, although modified in degree. A process that could be employed for the use of cracked fuels would make possible efficient utilization of all available fuel oils.

The conventional method of introducing fuel oil to most burners is by conveying the oil through a pipe or channel where the oil is in wetting contact with the pipe. In pot-type burners, the oil is allowed to flow from the pipe onto the bottom,

with the oil wetting the bottom of the burner. If the temperature of the pip r tt m is u that some vaporization of the oil is accomplished, then tarry residues may deposit upon the bottom and upon the pipe, and eventually may impede the flow of oil through the pipe. The collection of tarry residues in the burner limits the efficient life of the burner. Further, in existing types of oil burners, the mixing of fuel oil vapor with air is usually accomplished in a space where combustion of the vapor and air is taking place. This condition tends to prevent the adequate mixing of the vapor and air before combustion is initiated, and usually results in the formation of soot and smoky or yellow-colored flames. Cracked fuel oils particularly, which contain more aromatic and olefin hydrocarbons, either alone or in admixture with straight run fuels, cannot satisfactorily be handled in such equipment.

An object of the present invention is to provide new methods and apparatus for the vaporization and combustion of hydrocarbon distillates which will result in a minimum production of such residues which would tend to interfere with the operation of the process. Another object is to provide methods and means whereby cracked fuels, in addition to straight run fuels, may be vaporized, mixed with air, and subjected to a combustion process while maintaining the apparatus therefor in clean and efficient use over long periods of time. A still further object is to provide a process and apparatus for utilizing hydrocarbon distillate fuels by employing non-wetting vaporization on a hot surface under conditions which result in a minimum production of residues which if formed would interfere with the operation of the apparatus. Yet another object is to provide a process and apparatus in which an adequate mixing of fuel oil vapor and combustion oxygen is obtained before combustion of the mixture is allowed to take place, means being provided for preventing the flame from being propagated back into the vaporization and mixing zones. A further object is to provide a new method and means for introducing the oil to be vaporized with respect to the vaporizing surface whereby the feeding means for the liquid fuel is maintained at a relatively low or cool temperature so that residues do not form thereon, etc. Other specific objects and advantages will appear as the specification proceeds.

The current trend of opinion among those skilled in the art has followed mainly two patterns. One view is that temperatures in the vaporization zone should be kept low in order to prevent cracking and the accumulation of carbon deposits. Another view is that the burning of cracked oil fuels which contain more aromatic and olefine hydrocarbons should be avoided because of their tendency to build up tarry and coke deposits. Cauley and Linden state: Burner manufacturers have previously found that high temperatures in the bottom of pot-type burners were conducive to good operation with straight run fuels, whereas present studies have shown the reverse to be beneficial in combustion of aromatic fuels. A reorientation of ideas upon combustion in such burners is therefore indicated.

Griswold in Fuels, Combustion and Furnaces (1946) described on page 276, the art and difliculties as follows: vaporizing burners require light fuels which vaporize at temperatures below that at which appreciable thermal decomposition or cracking occurs. Nevertheless, carbon accumulates slowly, even with fuels as light as kerosene, necessitating periodical cleaning of the wick or pot.

Cauley and Linden ("Oil and Gas Journal, August 10, 1946), believe that radiant heat would speed up cracking of aromatics in the liquid state to such an extent that many molecules are likely to crack and join together before they vaporize. They designed a pot-type burner with a radiation shield near the bottom in an attempt to prevent this from occurring. They summarized their combustion studies of cracked fuel oils by stating, Combustion studies pointed to the desirability of a progressive type of oxidation of aromatics, if such could be achieved, and suggested lower temperatures during mixing of air and oil vapors.

Moyer in Oil, Fuels and Burners (193'?) page 84, states that, vaporizing burners are not well suited to burn the heavier oil fuels for the reason that they are likely to contain hydrocarbons which will not resist cracking before they reach the vaporizing temperature. When a large drop, or even a film, of oil comes into contact with the hot metal of the pot, the cracking is likely to occur in that part of the drop of oil which is nearest the highly heated surface, and in that case the rest of the oil in the drop forms a blanket between the solid products that result from cracking and the air, so that solid carbon is deposited in an unburned condition on the surface of the pot.

Heiple and Sullivan in their paper Mechanisms of Combustion and Their Relation to Oil Burner Design, presented at the annual meeting of American Society of Mechanical Engineers, December 1-5, 1947, made the following statement regarding this subject: Accordingly, the presence of olefins in fuel-oil distillates may give rise to tarry and coke-like deposits if the temperature to which unburned fuel is exposed should become excessively high.

We have discovered that liquid oil, including the cracked fuel oil distillates, may be efiiciently vaporized by feeding the oil onto a very hot surface, the temperature of the surface being so high as to prevent the liquid oil from wetting the surface when applied thereto. In one embodiment of our invention, oil is dropped or fed onto a hot surface maintained at a temperature at which the oil will not wet the surface and on which the oil forms in a drop or droplets, with each drop essentially surrounded on all sides by its own vapor. Under these conditions, where liquid fuel oil as such is probably never in contact with the hot surface, very little, if any, carbon,

4 asphalt or soot is formed due to the vaporization of the fuel oil.

We use the term Wetting in its usual meaning to describe the conditions existing when liquid fuel oil is in intimate contact with the vaporlZillg surface, forming an oil-surface interface. Similarl non-wetting is used to describe the conditions existing when liquid fuel oil is not in intimate contact with the vaporizing surface, and.

where the interfaces formed are probably vaporizing surface-gaseous fuel oil and gaseous fuel oil-liquid fuel oil. When liquid fuel oil does not wet a surface, it resembles the action of water on a very hot iron surface.

We have found that when fuel oil is in wettin contact with a steel surface whose temperature is such that an appreciable vaporization of the oil occurs, tarry residues are formed. However, if the fuel oil is in non-wetting contact with a steel surface whose temperature is such that vaporization of the oil occurs, very little, if any, tarry residue is deposited on the steel surface.

The processes contemplated herein may be practiced in a variety of forms of apparatus. One form of apparatus with which some embodiments of our processes may be used is set out in the accompanying drawing, in which- Figure 1 is a broken perspective-view of apparatus embodying our invention and with which some of the processes contemplated herein may be used; and Fig. 2, an enlarged broken sectional view of the heating surface illustrating the liquid drop or body which is supported above the surface by vapor, etc.

In the illustration given, liquid fuel from the supply tank I passes through the opening 2 of the feed tube forming a stream or series of drops of fuel oil 3. The oil drop or body 3 is allowed to fall toward the plate or heated surface 4. The member 4 is heated by a heater 5 to a temperature at which the oil will not wet the surface. It will be understood that any means for heating the surface to such a temperature may be employed.

A casing provides a chamber above the plate 4 for receiving the vapor. On one side, the casing is apertured to receive the outlet pipe of a blower 8. The outlet 1 of the pipe communicates with the chamber 6 at a point substantially above the surface 4 at which vaporization takes place.

Opposite the outlet I from the blower 8 is a mixing pipe 9 adapted to receive air and vapors and to convey them into a combustion chamber I0 provided by the casing II. The pipe 9 which extends into the casing H is provided at its end with a screen or grid I 2 which breaks up the stream into smallerstreams and prevents the flame within the chamber II] from being propagated back into the mixing pipe 9 and the vaporization chamber 6.

The casing ll may be provided with electrical contact members I3 which are spaced apart to provide a spark for igniting the fuel. A stack l4 communicates with the top of easing II.

In the illustration given in Fig. 2, the drop or body of oil 3 is illustrated as supported above and out of direct liquid contact with the surface 4 by a body of vapor l5 which tends to enclose the entire liquid drop or body.

In chamber ID, the combustion gases are ignited and the flame therein is prevented from being propagated back into the pipe 9 and chamber 6 by a grid I2. If desired, the grid may be removed and the position of flame stabilizedin 5 chamber it by providing arelatively high. velocity of flow through the pipe 9.

By dropping the liquid oil in a continuous stream or series of droplets from a pipe or tube whose; outer end or lip not. connected tothe hot portions of the vaporizing: surface, we find that there is: no tendency for tarry residues to collect about the pipe which would impede the flow of the oil. In the structure illustrated, the outlet tip of the feed tube is relatively cool and tarry residues do not form thereon.

Further, by maintaining a vaporizing. zone and. a. mixing zone so that adequate mixing of the fuel oil vapor and combustion oxygen is obtained before combustion of the mixture is allowed totake place, we find that blue flame combustion is: obtained. The heating, of the oxygen or air the. mixing chamber prior to its admission. into the combustion chamber further aids in the-com.- bustion by preventing the condensation; of oil vapor on surfaces in. the mixing chamber.

By dropping the oil upon the hot surface maintained at non-wetting temperatures in a va porizing chamber separate from the combustion chamber, effective vaporization is brought about without formation of appreciable carbon, soot or tarry residues. The oil is thus fed from a sep arate relatively cool source and is: not subjected to temperatures which tend to form such objectionable residues. The oil may be fed by gravity in a continuous stream or drop-wise or it may be discharged under pressure in the form of separate streams or drops upon the vaporizing surface.

By thoroughly mixing the vapors thus produced with air before any flame is allowed to form and then igniting the mixture in a separate combustion chamber, it is possible to produce smoke-free flames.- In conventional burners of any type, the. efficiencies are limited by the smoke that can be tolerated- In a burner incorporating our invention it is possible to obtain significantly higher combustion efliciency because the production of smoke is not the limiting factor.

In connection with a number of specific examples, fuel oils, as described in the table herebelow, were vaporized in an apparatus similar to that illustrated in Fig. 1, which permitted weighing of the vaporization residues when 200 m1. of

each of these fuels were vaporized on surfaces such as porcelain or stainless steel.

TABLE A. S. T. M

n n 1 Derby Mobilbeat.

Property 1 Na Ezigol gel Initial Boiling Point. F 329 364 417 10 7,: Boiling Point, F. 400 429 459 50% Boiling Point, F 466 484 505 95% Boiling Point, F- 552 578 I 626 End Boiling Point. F 560 624 68E A. P. I. Gravity. 41-.8 33.3 V 28.7 Aniline Number. F 158.1 135.0 117'. 3 Carbon Hydrogen Rntio.- 5L6 n80 7.32 Diesel Index 66; S- 45 33; 2

vaporization tests were made when the vaporizing surfaces were maintained; at one set temperature in the range from 450 F, to 1200 F. in atmospheres of air, nitrogen. oxygen, and steam. The test apparatus was provided with a heated jacket having an observation window, andv temperature observations were made by means of thermocouples in the spaces, and also with thermocouples welded or cemented to the vaporizing surfaces. All references to temperatures are made to these measurements performed with ordinary laboratory equipment. and techniques. Provision was also made to analyze certain changes in composition during the vapor phase reactions.

The following specific tests were made. and the conditions and results may be. set out as follows:

Example 1 Two hundred ml. of. the first fuel shown in the table. which is a straight run distillate having an initial boiling point of 329 FL, were vaporized on a porcelain surface maintained at 450 FL, as indicated by use of an iron-constantan thermocouple cemented to the porcelain surface. The fuel oil was dropped on the heated surface. Visual observation indicated that the oil wetted the porcelain surface. The resulting vapors were sucked off and condensed. It should be pointed out that this vaporization processoccurred inv the presence of'atmospheri'c' oxygen, which in all tests was heated to the same temperature as that of the vaporizing surface. An asphaltic or tarrylike residue, weighing 25.6 milligram-s, wasform'ect on the porcelain surface. Exactly the sameexperiment was repeated, except the temperatureof the porcelain surface was maintained at- 650" F;

.A similar residue of L6 milligrams was formed,

and visual observation indicated that the oil was still wetting the porcelain surface. The same experiment was repeated; except the temperature of the porcelain surface was maintaned at 800 FL, resulting in 1.0 milligram residue, and wetting conditions where still observed. In the next experiment, 200 ml. of this fuel oilwere vaporized on a porcelain surfacemaintained at 950 F., atmospheric air was preheated to a similar temperature, and the" resulting oil vapors sucked or blown away from the vaporizing surface. Visual observation indicated that this fuel oil did hot wet the. 950 F. porcelain surface, but formed small droplets which skidded over the" porcelain surface until. completely vaporized. No detectable amount of the vaporization residue was found on the porcelain surface.

Example 2 Another set of experiments was performed, using the second; fuel oil in the table, which was a cracked fuel and. had an initial boiling point of 364 F. This oil is typical of commercially available cracked fuel oils. Two hundred ml. of the oil were vaporizedv on a porcelain surface main.- tained at 650 F., and inanair atmosphere main tallied at the same temperature. The resulting fuel oil vapors were blown away from the vaporizing surface. Visual observation indicated that wetting conditions prevailed. The vaporization residue was 89.6 milligrams. The same experiment was repeated, except that the porcelain surface and air temperatures were maintained at 800 F. Wetting conditions prevailed and the vaporization residue was 47 .8 milligrams- The experiment was again repeated, using 950 F. porcelain and air temperatures. Visual observation indicated that non-wetting conditions prevailed and nodetectable vaporization residues were found. The same set of three experiments was duplicated, i. e., 650 800 F. and, 950 F. experiments, except that the vaporization process was carriedout in a nitrogen atmosphere maintained at the appropriate temperatures. At 650 F. and800 R, wetting conditions. prevailed and the residueswere 46.6 and 47.8 milligrams respectively. At 950 F., non-wetting conditionsprevailed and no detectable residue was found.

Another similar series of experiments was performed using stainless steel vaporizing surfaces maintained at indicated temperatures of 750 F., 800 F. and 950 F., and in the presence of air preheated to the corresponding temperatures. The surface temperatures were measured by means of iron-constantan thermocouples brazed to the surface. Visual observation indicated that wetting conditions prevailed at 750 F. and non-wetting conditions prevailed at 800 F. and 950 F. The vaporization residue weighed 84.0 milligrams in the 750 F. experiment, and no detectable residues were found in the 800 F. and 950 F. experiments. Example 3 The third fuel oil shown in the table, which is also a cracked oil and has an initial boiling point of 417 F., was tested in a series of experiments. This fuel oil probably contains as high a percentage of aromatic and olefin hydrocarbons as any fuel oil that is at present commercially available. Two hundred m1. of A. S. T. M. reference fuel oil No. 2 was vaporized on a porcelain surface maintained at 800 F. and in an air atmosphere maintained at the same temperature. Visual observations indicated that wetting conditions prevailed, and a vaporization residue weighing 152.8 milligrams was found. The same experiment was repeated, except that the vaporizing surface and air temperature was maintained at 950 F. Visual observations indicated that non-wetting conditions prevailed and no detectable residues were found.

Example 4 The second oil shown in the table was again tested in another set of experiments, using apparatus like that shown in Fig. 1. This oil was vaporized at rates between 3 to ml. per minute under non-wetting conditions. The resulting oil vapors were mixed with the combustion oxygen in the mixing chamber and ignited at the grid. Different lengths of mixing chambers were employed to determine the minimum length in which adequate mixing could be obtained. In this particular experiment, the minimum length was found to be approximately 18 inches of 2- inch diameter tube when vaporizing oil at a rate of 6 ml. per minute and providing sufficient combustion oxygen so that the resulting carbon dioxide content of the flue gases was between 10% and 14%. Blue flame combustion was obtained under these conditions, and no detectable amount of soot was found in the combustion chamber. Likewise, the flue gases, measured by the Icham smoke meter, were 100% clear. Mixing tubes of shorter length were used by increasing the turbulence by means of spirals, rotating disks, and offcenter air inlets. We have found that adequate mixing of the air and vapors can be accomplished by a variety of well-known means.

In all of the foregoing examples, no detectable quantities of soot were found. By careful regulation of the ratios of fuel vapor to air, 100% blue flames were attained when the carbon dioxide percentage of the blue gases was 14.7%. Constant production of the blue flame, which at the same time produces 14.7% carbon dioxide, was believed to be the result of vaporizing in the manner already described and the mixing of the vapors with air before the mixture was ignited. In additional experiments, we have further increased the ratio of fuel oil vapor to combustion oxygen such that the resulting flue gases analyzed 11% to 12% carbon dioxide, 4% to 6% carbon monoxide, and 0% oxygen. The flames in such experiments were 100% blue. From these we believe that adequate mixing of fuel oil vapor and combustion oxygen is a primary factor in eliminating the formation of soot or smoke.

Some of the foregoing experiments were performed with a metallic grid separating the combustion chamber from the mixing chamber. In other experiments, we dispensed with the use of the grid by increasing the velocity of the combustible mixture in the mixing chamber which prevented the combustion taking place until the velocity was decreased by expansion of the mixture into the combustion chamber. This again resulted in 100% blue flames and no detectable formation of soot or smoke. The temperatures of the walls of the mixing chambers were preferably maintained high enough to prevent condensation of the fuel oil vapor on the walls, and the maintenance of such temperatures was made easy by the preheating of the combustion oxygen.

In the practice of the invention with different types of oils, it is found that the wetting temperatures and non-wetting temperatures vary with the different oils. It is therefore not possible to set out a specific temperature which may be designated as the initial non-wetting temperature for all the oils. Generally, we find that with commercially available fuel oils whose boiling point is under 700 F. (similar to the oils in the table), the initial non-wetting temperature on a steel surface lies above 700 F. With heavier fuel oils, the initial non-wetting temperature may be as high as 1500 F. For most of the fuel oils of the type described herein, we find that the non-wetting temperature is above 700 F., and we prefer to maintain the temperature below 1500 F. Where oxygen is present, we prefer to maintain the temperatures below 1200 F. However, ignition of the vaporized oil within chamber 6 is substantially controlled in our method of operation by causing the vaporized oil to meet the stream of air considerably above the vaporizing surface 4. Thus, a high concentration of vaporized fuel oil is maintained in the lower portion of chamber 6, which thereby effectively envelopes and shields the vaporizing surface as well as the hotter side walls bounding the lower portion of the vaporizing chamber. Furthermore, it will be understood that the exact ignition temperature for any given fuel-air mixture depends not only on the centration of fuel in the mixture, but also on the time of exposure to this temperature. In tests to determine the temperatures required within chamber 6 to cause actual combustion, it was found that an average temperature of around 2000 F. was required. The lowest temperature at which such combustion was obtained with any of the oils mentioned herein was 1860 F. The initial non-wetting temperature for any fuel oil is easily determined in a moment by dropping the oil upon a hot plate whose temperature is being raised between about 700 F. and 1500 F. and observing when the oil ceases to wet the surface and begins to dance upon the surface. For commercial purposes, the temperature of the surface should be held substantially above the initial non-wetting temperature.

The No. 1 oil indicated in the table was found to have an initial non-avertin 1 perature of 725 The Mob'iih'eat No. 2 011 was found to have an initial non wetti-ng temperature of 760' F. The A. s. "-I. reference 011 had initial non wet'ting temperature er 825 F. Heavier oils were round to have substantially higher initial non-wetting temperatures. I t

the operation described, the v'poraat on was carried on at atmos heric pressure; and it Will be noted that the feed line was preteete against heat by the new of air introduced by the mower. I A

While inthe practice of the inve t-mama prefor to employ a non-wetting temperature for the oil, it will be understood that there are tom'- peratures which are substantially non-wetting temperatures or so close thereto that an appreciab'le accumulation of carbon which would in terfere with the operation does notbccur; and such conditions are contemplated being a part of the invention herewith.

Further specific examples may be set out as follows:

drops of oil did not wet the vaporizing surface. The vaporization residue averaged 0.03 gm. per

gallon of fuel consumed. This is in contrast to approximately 4.0 gm. per gallon-of residue produced in conventional vaporizing burners under the same condition. The performance of the burner was also superior to the conventional vaporizing burner in other respects. The measured carbon dioxide was 14.7% and less than 0.05% carbon monoxide, with an indicated combustion efficiency of approximately 82%. The smoke measurement was 100% clear as measured by the I'cha'm tests.

Example 6 A natural draft type of burner was constructed which incorporated our processes for introducing the oil and vaporizing the oil under nonwetting conditions. This burner operated at a rate of 35,000 B. t. u. per hour using catalytically cracked fuel. In this burner, the velocity of the air and fuel vapor mixture was used to maintain the flame away from the vaporization zones and from the zones where the fuel vapors and air were first mixed.

While in the foregoing specification, we have set forth specific embodiments of our invention in great detail for the purpose of illustrating the invention, it will be understood that the details or steps in the embodiments described and the details of structure in the appaartus set out may be varied widely by those skilled in the art without departing from the spirit of our invention.

We claim:

1. In the preparation of a combustible mixture containing oxygen and fuel oil vapors, the method of vaporizing a liquid fuel oil characterized by the step of dropping liquid fuel oil upon a heated surface within a restricted zone from a point above said surface, said fuel oil having a 90% boiling point under 700 F., said heated surface i 0 being continuously maintained at a tn'lpfatuife above 700 F. at which the fuel oil to be vaporiZ'ed does hot wet s "6. surface but below a temperature at which lg t'ioii occurs.

2. In the pi-epaiavien Of a combustible tare eosteiniag oxygen are; an vapors, the steps of -vapbr'izing" l-i' 'id fuel oil in a restricted vaporization zone by directing the -liquid fuel 611 men a hearse airtime-genius: on having a boiling point under 700 said surface being continual-1y maintained at a temperature above 7-00 F. at which'the fuel oil to be vaporized does hot wet said surfaceas ev dences bythe dancing of drops of Said hiei Oil on said surface but below a temperature at which ignition occurs, passing the fuel oil vapors to a mixing zone spaced from said surface, "and mixin therein an okygh containing gas with said fuel oil vapors. r

3. In the preparation of a combustible mixture containin ex geii and fuel oil vapors jfrorn cracked fuel oils, the steps of vaporizing liquid fueloil of the cracked ty'p'e a restricted vaporizationzone by directing the liquid fuel oil upiin a heated surface, said cracked fuel oil having a 90% boiling point under 700 F., said surface being continually maintained at a temperature above 700" F. at which the fuel oil to be vapori'zed does not wet said surface but bel a ternperature at which ignition occurs, pas V the fuel oil vapors to amixing zone spaced from said surface, and mak ng therein an oxygen containing gas with said fuel oil vapors.

4-. In the preparation of a combustible mirture containing oxygen and fuel oil vapors, the steps of vaporizing liquid fuel oil in a restr cte vaporization zone by directing the liquid fuel oil upon a heated surface, said liquid fuel oil having a 90% boiling oint und r 700 F., said surfae'e being continually maintained at a temps; ure above 700 F; at which the fliel oil to be vaporized does not wet said surface but below'a tendperatur'e' at which ignition occurs, passing the fuel oil vaporsto a inixingzone spaced from said surface, and mixing therein an oxygen containing gas with said fuel oil vapors said heated surface being shielded against said oxygencontairiing gas b'y'the intervening fuel oil vapors.

5. In the preparation of a combusible mixture containing oxygen and fuel oil vapors, the steps of forming an upwardly rising mass of fuel oil vapor by directing liquid fuel oil upon a heated surface within a restricted zone, said liquid fuel oil having a 90% boiling point under 700 F., said surface being continuously maintained at a temperature above 700 F. at which the fuel oil to be vaporized does not wet said surface but below a temperature at which ignition of the mass of fuel oil vapor occurs, meeting the upwardly rising vapor mass with a stream of oxygen containing gas at a point above said surface so that said vapor mass substantially shields said heated surface against the direct blast of said oxygen containing gas.

6. In the preparation of a combustible mixture containing oxygen and fuel oil vapors, the steps of forming an upwardly rising mass of concentrated fuel oil vapor by directing liquid fuel oil upon a heated surface within a restricted zone, said liquid fuel oil having a 90% boiling point under 700 F., said surface being continously maintained at a temperature above 700 F. at which the fuel oil to be vaporized does not wet said surface but below a temperature at which ignition occurs, meeting the upwardly rising vapor mass with a stream of air directed into a separate mixing zone, and thereafter thoroughvly mixing said air with said vapor mass.

7. In the preparation of a combustible mixture containing oxygen and fuel oil vapors, the steps of forming an upwardly rising mass of fuel oil vapor by directing liquid fuel oil upon a heated surface within a restricted zone, said liquid fuel oil having a 90% boiling point under 700 F., said surface being continuously maintained at a temperature above 700 F. at which the fuel oil to be vaporized does not wet said surface but below a temperature at which ignition of the mass of fuel oil vapor occurs, meeting the upwardly rising vapor mass with a stream of air directed away from said heated surface, whereby said vapor mass serves to substantially shield said heated surface from contact with dilute mixtures of vaporized fuel and air.

8. In the preparation of a combustible mixture containing oxygen and fuel oil vapors, the

steps of forming an upwardly rising mass of concentrated fuel oil vapor by directing drops of liquid fuel oil upon a heated surface within a restricted zone, said liquid fuel oil having a 90% boiling point under 700 F., said surface being continuously maintained at a temperature above 700" F. at which the fuel oil to be vaporized does not wet said surface as evidenced by the dancing of drops of fuel oil on said surface but below a temperature at which ignition occurs, meeting mixing zone, and thereafter thoroughly mixing a said stream of air with said vapor mass.

9. In the preparation of a combustible mixture containing oxygen and fuel oil vapors from cracked fuel oils, the steps of forming an upwardly rising column of concentrated fuel oil vapor by dropping liquid fuel oil of the cracked type upon a heated surface within a restricted zone from a point spaced above said surface, said cracked fuel oil having a 90% boiling point under 700 F., said heated surface being continuously maintained at a temperature above 700 F. at which the fuel oil to be vaporized does not wet said surface as evidenced by the dancingof drops of said fuel oil on said surface but below a temperature at which ignition occurs, meeting the upwardly rising concentrated vapor mass with a stream of air at a point above said heated surface, said stream of air being directed away from said heated surface and into a separate mixing zone, and thereafter thoroughly mixing said stream of air with said vapor mass.

10. In the preparation of a combustible mixture containing oxygen and fuel oil vapors from cracked fuel oils, the method of vaporization characterized by the step of directing drops of liquid fuel oil of the cracked type upon a heated surface within a vaporization zone, said cracked fuel oil having a 90% boiling point under 700 F.,

said surface being continuously maintained at a temperature above 700 F. at which the fuel oil to be vaporized does not wet said surface but below a temperature at which ignition occurs.

EDWIN C. HYATT. LUTHER L. LYON, JR. WILLIS R. SWANSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,214,838 Staude Feb. 6, 1917 1,744,111 French Jan. 21, 1930 1,754,136 Woidick Apr. 8, 1930 1,767,295 Lee June 24, 1930 1,959,031 Masters May 15, 193 1,966,610 Chilowsky July 17, 1934 2,039,790 French May 5, 1936' 2,212,061 Dalen et al. Aug. 20, 1940 2,216,178 Astradsson Oct. 1, 1940 2,256,785 Dalen et a1 Sept. 23, 1941 FOREIGN PATENTS Number Country Date 719,526 France Nov. 23, 1931 OTHER REFERENCES Ganots Elementary Treatise on Physics, 18th Edition, Publ. by Longmans, Green and Co., 1910, Section 392, pages 393 to 395. 

1. IN THE PREPARATION OF A COMBUSTIBLE MIXTURE CONTAINING OXYGEN AND FUEL OIL CHARACTERIZED BY OD OF VAPORIZING A LIQUID FUEL OIL UPON A HEATED THE STEP OF DROPPING LIQUID FUEL OIL UPON A HEATED SURFACE WITHIN A RESTRICTED ZONE FROM A POINT ABOVE SAID SURFACE, SAID FUEL OIL HAVING A 90% BOILING POINT UNDER 700* F., SAID HEATED SURFACE BEING CONTINUOUSLY MAINTAINED AT A TEMPERATURE ABOVE 700* F. AT WHICH THE FUEL OIL TO BE VAPORIZED DOES NOT WET SAID SURFACE BUT BELOW A TEMPERATURE AT WHICH IGNITION OCCURS. 